Seagrass blue carbon dynamics in the Gulf of Mexico: Stocks, losses from anthropogenic disturbance, and gains through seagrass restoration.

Seagrasses comprise a substantive North American and Caribbean Sea blue carbon sink. Yet fine-scale estimates of seagrass carbon stocks, fluxes from anthropogenic disturbances, and potential gains in sedimentary carbon from seagrass restoration are lacking for most of the Western Hemisphere. To begin to fill this knowledge gap in the subtropics and tropics, we quantified organic carbon (C) stocks, losses, and gains from restorations at 8 previously-disturbed seagrass sites around the Gulf of Mexico (GoM) (n=128 cores). Mean natural seagrass C stocks were 25.7±6.7MgCha around the GoM, while mean C stocks at adjacent barren sites that had previously hosted seagrass were 17.8MgCha. Restored seagrass beds contained a mean of 38.7±13.1MgCha. Mean C losses differed by anthropogenic impact type, but averaged 20.98±7.14MgCha. C gains from seagrass restoration averaged 20.96±8.59Mgha. These results, when combined with the similarity between natural and restored C content, highlight the potential of seagrass restoration for mitigating seagrass C losses from prior impact events. Our GoM basin-wide estimates of natural C totaled ~36.4Tg for the 947,327ha for the USA-GoM. Including Mexico, the total basin contained an estimated 37.2-37.5Tg C. Regional US-GoM losses totaled 21.69Tg C. C losses differed significantly among anthropogenic impacts. Yet, seagrass restoration appears to be an important climate change mitigation strategy that could be implemented elsewhere throughout the tropics and subtropics.